Requirements for stimulation of autoreactive T cells by thymic stroma

Thymic stromal cells are more efficient than similarly treated spleen cells for Ag presentation to Ag-specific, MHC-restricted T cell lines. Thymic stromal cells fail, however, to stimulate proliferation of autoreactive T cell lines. This failure to stimulate autoreactive T cells does not appear to be due to tolerance induction because thymic stroma does not interfere with subsequent stimulation by spleen cells. Moreover, the ability of thymic stromal cells to stimulate autoreactive T cells can be restored by addition of exogenous IL-1. This demonstrates that the specific self-determinants recognized by autoreactive T cells can be expressed on thymic stromal cells. Failure of stimulation by thymic stromal cells in the absence of exogenous IL-1 may reflect a difference in the physiologic requirements for activation of autoreactive T cells as compared to Ag-specific, MHC-restricted T cells.